Safety interlock for electrical and mechanical equipment and systems



R. L. KIRK Dec. 29, 1936.

SAFETY INTERLOCK FOR ELECTRICAL AND MECHANICAL EQUIPMENT AND SYSTEMS Filed Nov. 4, 1931 Patented Dec. 29, 1936 UNITED STATES PATENT OFFICE SAFETY INTERLOCK FOR ELECTRICAL AND MECHANICAL EQUIPMENT AND SYSTEMS as trustee Application November 4, 1931, Serial No. 572,998

1 o Claims. (01. 171-91) This invention relates to safety interlock systems and involves the application of special locks to standard electrical or mechanical equipment so as to require predetermined operation thereof, or operation in a predetermined sequence, to insure the safety of operators and workers, and

others who may have occasion to work upon the electrical or mechanical equipment, or upon associated circuits and apparatus, or to insure the safe operation of equipment or the safe production of materials.

One object of this invention is to provide an interlocking system for an electrical circuit containing a circuit breaker and one or more disconnect switches, whereby the control or operating mechanism of the circuit breaker may be locked in non-operating positions, so that an operator may safely work upon a circuit without the danger of an unauthorized or accidental reclosure of the circuit breaker with a resulting energization of the circuit. 7

Another object of the invention is to-provide an interlocking system whereby the circuit breaker must be opened and locked in its open position, before access may be had to the disconnect switches, associated with the breaker, and before the switches may be opened and locked in open position.

Another object of the invention is to provide an interlocking system in which a special actuating key element for stick-operating disconnect switches, or standard type lock key for gangoperated disconnect switches of a circuit, may be made available only after the associated circuit breaker has been opened and locked in its open position.

Another object of the invention is to provide novel locking devices for general applications and to permit sequence interlocking in a power distribution system, or in a production system to insure the safety of operators or of the mate rials being produced.

One aspect of the invention involves a system in which a key cannot be removed from the control lock except when the lock and the controlled apparatus are in pre-selected safety positions.

The control equipment must therefore always be locked in a predetermined position before the key can be removed to lock, unlock, or operate other associated apparatus.

Another aspect of the invention involves the utilization of looks with key-operated locking bolts to lock apparatus, or operating mechanism therefor, in predetermined safety positions. The locking bolts when so used a e O 1 31016 11 length to extend into slots or holes in the apparatus or associated mechanism to lock the apparatus or mechanism in a selected position.

In an electrical system, for example, the op erating mechanism of an oil circuit breaker must first be actuated to open position, and then looked in such open position, before one or more associated disconnect switches can be opened. Those switches, in turn, must be locked in open position before a door leading to the oil circuit breaker compartment can be unlocked. After the desired work has been completed, such as repair, adjustment, etc., the reverse sequence of operation is required to re-establish the operating condition of the system, namely, locking the door to the oil circuit breaker compartment, then closing the disconnect switch or switches and then finally closing the oil circuit breaker itself. In such arrangement, each safety locking operation releases a key to permit access to, or operationof, an associatedpiece of apparatus in a predetermined sequence which insures the safety of the operator or the safe operation of the equipment. The nature of the sequence of operations necessary, will depend upon the system to which the interlocking system is applied.

In a mechanical system the interlocks would provide for looking a steam valve closed, for example, in a piping system before other valves could be opened, or before access could be'had to any closure into which the piping system would feed when the valve was opened.

Another object of the invention, in its application to an electrical system, is the provision of a specially shaped key bolt to operate individual blades of stick-operated disconnect switches. The key bolt is normally held in the lock mechanism associated with a circuit breaker mechanism and is released only when the circuit breaker mechanism is locked in its open position. The key bolt is shaped to fit into a complementarily shaped operating head in the disconnect switch associated with the same circuit as the circuit breaker. By such arrangement this key bolt will fit only into the head of the associated disconnect switch.

Since the disconnect switch is normally energized and is ordinarily mounted somedistance above ground and must be operated through the medium of a disconnect stick, which is a long wooden handle, to provide a maximum degree of insulation between the operator and the switch, I have provided on the end of the disconnect stick a specially constructed supporting head so the key bolt may be readily positioned in its registering position, at which it will fit into the head of the disconnect switch.

The key bolt is further so constructed that its presence is necessary in the lock on the circuit breaker in order to permit the lock to move to its non-locking position, so that the circuit breaker may be reclosed.

In the present application I have illustrated several uses or applications of the interlocking system, wherein the safety feature is highly desirable, and wherein it may be easily and readily attained, by means of the devices illustrated, or by other devices employing similar principles. The principles of my invention and its applications are illustrated in the accompanying drawing, in which Figure l is a diagrammatic view of a circuit breaker control system illustrating the disposition of the barrier lock for controlling the trip-free mechanism of the circuit breaker;

Figure 2 is a side elevational view of the operating arm of the mechanism, upon which a locking barrier has been mounted to control the effectiveness of the latching trigger by means of which the trip-free lever is maintained in operative re laticnship;

Figure 3 is a sectional view of the structure shown in Figure 2, taken along the line 3-3, and

, illustrates the manner in which the lock is mounted upon the frame of the operating arm;

Figure 4 is a side elevational view of a nontrip-free type of operating mechanism for an oil circuit breaker;

Figure 5 is an enlarged view of a portion of the mechanism in Figure 4, illustrating the application of a barrier to the mechanism to control the operativeness thereof;

Figure 6 is a sectional view of the mechanism shown in Figure 5, and illustrates the manner in which the lock is applied to the mechanical structure so that the barrier controlled by the lock may render the mechanism operative or nonoperative.

As shown in Figure 1, one type of actuating mechanism for an oil circuit breaker comprises a closing coil structure I and a trip coil structure 2 constituting part of a metal frame structure I. The closing coil operates upon a trip-free lever assembly including an actuating lever 4 and a tripfree lever 5, the latter of which is directly connected to a connecting rod 6 which operates the contact members of the circuit breaker (not shown).

As is well-known to those skilled in the art, the two levers 4 and 5 are relatively movable with respect to each other, so that under abnormal conditions the lever 5 may release itself from the actuating lever 4. Normally the tripfree lever 5 is mechanically connected to the actuating lever 4 by means of a biassed latching trigger l which is normally biassed to latch and engage a pin or roller 8 at the end of the pivoted trip-free lever 5. The latching trigger 1 is pivotally mounted on the actuating lever 4. When the actuating lever 4 has been moved to its furthermost downward position by the closing coil or by a handle IS, the lever 4 is latched and held in such downward position by a holding latch 9 that fits into and engages a recessed shoulder ll near the end of the actuating lever 4. As is illustrated, the plunger l2 associated with the closing coil l is mechanically connected to the actuating lever 4 at the pivot point l3. The plunger l4 of the trip'coil 2, however, is not mechanically connected to the lever mechanism, but serves,

when raised by the trip coil 2, to actuate or strike the lower arm of the latching trigger I to cause the trigger 1 to disengage the pin I on the trip-free lever B, thereupon permitting lever B to rise to the position illustrated. The circuit breaker contacts are then permitted to be opened under the tension of blessing springs provided for that purpose, but not illustrated in this drawing since they are not part of this invention and are well recognized as constituent parts of a circuit breaker.

In order to operate the mechanism manually in case of emergency, such as failure of electric energy for the closing coil, the handle I! is provided, as shown, that fits into a socket at the end of the actuating lever 4 and is removable when not needed. It will be apparent from the foregoing description and the function of the latching trigger l, which holds the two levers 4 and 5 in mechanical connection, that the circuit breaker cannot be closed unless that mechanical connection is established between the two levers 4 and 5. If, therefore, the latching trigger I is locked in its non-engaging position with respect to the pin 8 on the trip-free lever 5, the trip-free lever I will remain in its open position, and operation of the actuating lever 4 will be ineffective to operate the circuit breaker contacts or to move them the slightest degree.

The ultimate safety feature that is desired, and that is to be accomplished in a protective system of this character in connection with circuit breakers, is to prevent the circuit breaker from being closed even momentarily, so that the circuit to which it is connected cannot be energized even for a moment while workmen are working upon any part of the circuit for the purpose of repairs, etc. I therefore provide the lock I. to be mounted on the actuating lever 4 adjacent the trigger latch I. As shown in Figure 2 the lock I 8 is provided with a key operable tumbler of any usual, well-known type, which in its movement will operate a bolt ll that has a barrier arm I8 secured to, or integral with, the end of the bolt H. The frame or tumbler of the lock casing is so arranged that the key cannot be removed from the lock except when, or until, the bolt l1 and the barrier arm l8 have been moved to such a position as to move the latching trigger 1 to its non-engaging position. In that position the trigger I cannot engage the pin 8 on the lever 5, and any electrical or mechanical actuation of the actuating lever 4 would be ineffective to close the circuit breaker or even to start the closing action of the circuit breaker contacts, thereby giving complete protection against the unauthorized closing of the breaker when the lock key is removed.

As is illustrated in Figure 3, the actuating lever 4 usually embodies a double wall structure between which the latching trigger l is pivotally supported.

The circuit breakeris usually connected in a circuit which is provided with disconnect switches to isolate the circuit breaker, to per mit it to be repaired or otherwise worked upon. The key is, which is removable from the lock only when the circuit breaker is locked open, at the latching trigger I, may be used to open a door to the disconnect switch compartment, or for any use, such as the unlocking of disconnect switch control handles, etc.

when the trip-free and actuating arms 4 and 5 are engaged and the breaker is closed, the friction of the latching trigger cannot be readily overcome by the action of the lock and key i9, so that the breaker must be opened otherwisein a usual manner before the key can be removed.

Figure 4 shows an older and less modern type of actuating mechanism for a circuit breaker. This mechanism is not provided with the tripi'ree lever, and the circuit breaker may be closed and held closed upon a short circuit if the closing coil is kept energized, or the hand actuating lever held down due to the absence of the trip-tree mechanism which would permit the disconnection of the actuating mechanism under abnormal conditions.

In order to prevent such operation of this mechanism as shown in Figure 4, a blocking barrier is provided as illustrated in Figures and 6. As shown in those figures, the lock I6 is mounted on a steel bracket 25 attached to the frame, and a pivoted barrier 26 is controlled by the lock bolt l1 so that the barrier may be moved into or out of the path of movement of the actuating lever l to which the closing coil plunger 1 2 is connected. When the barrier 26 is moved to, and locked in opposing or barring position, as illustrated by the dotted lines in Figure 6, the actuating lever 4 cannot be moved downward to cause the closing of the circuit breaker contacts. When the barrier 26 is in such blocking position, the key I! may be readily removed from the lock, but in the other or normal position the key cannot be removed.

The lock is also provided with a switch 22, for this application, by means of which the circuit of the closing coil is also locked open, so that the operating lever 4 cannot be operated electrically.

As shown in Figure 4, the holding latch 9 is provided with an extendingarm 9a which is located in the path of the trip coil plunger, which actuates the latch 9 to release the actuating lever 4, so that that lever may move upward, when not held down, however, by the closing coil l or by a hand lever. The lock which is illustrated in Figures 5 and 6 could be applied to the holding latch 9 of the mechanism in Figure 4, in the same manner as applied to the latching trigger I in Figures2 and 3, but when so applied would not serve to prevent hand movement of the actuating lever 4 to the closed position 01' the circuit breaker, even though it would prevent latching the breaker closed. Therefore, for nontrip-free mechanism, the blocking barrier of Figure 6 is used, together with the switch for opening the circuit of the closing coll, giving the same perfection protection for non-trip-free as for trip-free mechanism, in that in either case the breaker cannot be closed even momentarily when the safety key is removed.

In mounting the lock for this application, Figure 6, the blocking barrier 26 is pivotally supported upon a base bracket 21 that is arranged to rest upon, and thus be supported by, the rigid frame 3 of the structure.

In all 01' the locks illustrated in the foregoing applications, the lock casing is intended to be made in such manner that it cannot be readily opened to permit access to the internal mechanism, and is to be riveted or welded in place.

so it cannot be easily removed. The bolt l1 and the barrier arm l8, as well as the blocking barrier 26 and its supporting brackets 25 and 21 are all intended to be of steel or cast steel parts, and are relatively strong and will not permit easy breaking, in order to insure a full and complete measure of safety to prevent the operation oi a circuit breaker when such operation is not desired, or would be dangerous to the life of workmen working upon a supposedly unenergized circuit.

In the foregoing description, I have illustrated and described the application of the locking barrier to latching triggers and holding latches in mechanism employed for controlling electrical circuits. This arrangement may also be employed in controlling the operation of machines or the relationship between co-operating mechanical parts for other purposes, and the present showing may be considered as illus trative of the principle broadly.

The employment or a hand stick and a spe cially shaped key element for operating a remotely located device may likewise be utilized for other purposes besides operating disconnect switches.

I desire it to be understood, therefore, that I do not consider my invention to be limited to the specific applications, or details of construction or assembly, as illustrated herein, since they may be variously modified without departing from the spirit and scope 01' the invention as set forth in the appended claims.

I claim as my invention:

1. In an interlocking system for an electrical system of distribution, the combination with a circuit breaker having a closing mechanism and a latching member that serves, when latched, to allow the breaker to be closed, or that serves to hold the closing mechanism in a position to maintain the breaker closed, of a barrier mov able into, and out of the path of movement of the latching member, a key-operated lock for moving the barrier, and a key for the lock arranged to be removable from the lock only when the latching member is moved to a non-lat hing position by the lock operated barrier.-

2. In an interlocking system for an electrical system of distribution, the combination with a circuit breaker having a closing mechanism and a latching member for holding the closing mechanism in. a position to permitthe breaker to be closed electrically or mechanically, of means for preventing or permitting electrical or mechanical closure of the breaker comprising a barrier movable into, and out of, the path of movement of the latching member, a key-oper able bolt secured to, or integral with the barrier to actuate .it, and a key for the lock removable only when the barrier is in closure-preventing position.

3. In an interlocking system for an electrical system of distribution, the combination with a circuit breaker having a closing mechanism, manual actuating means therefor and an electrically energizable device for actuating the closing mechanism, of means for preventing electrical or mechanical operation of the breaker, said means consisting of a barrier movable into and out of the path of the closing mechanism, a switching device for controlling the circuit of the electrical actuating device, and a key operable closing mechanism, and an associated subsidiary device whose operation is to be dependent upon prior positioning of the main device in a deenergized position; of means for mechanically blocking the main circuit-controlling device, and means for controlling the electrically energizable device to prevent electrical or mechanical actuation of the main circuit-controlling device from said de-energized position to an energized position, and a key for operating said means and arranged to be released when said means is in mechanical and electrical blocking position, and means associated with said subsidiary device operable by said key to permit access to or actuation of said subsidiary device.

5. In a mechanical system, the combination with a mechanical device having a latching member to permit operation of an associated member, of means for preventing or permitting operation of the associated member, comprising a barrier moving into and out of the path of the latching member, a key-operable lock for moving the barrier, and a key for the lock arranged to be removable from the lock only when the latching member is moved to the non-latching position by the lock-operated barrier.

. In a mechanical system, the combination with a mechanical device having a latching member to permit a mechanical member to be latched in a normal holding position, of means for preventing the latching in normal holding position, consisting of a barrier movable into and out of the path of the latching member, a key operated lock for moving the barrier, and a key for the lock, arranged to be removable from the look only when the latching member is moved to a non-latching position by the lock operated barrier.

7. In an electrical circuit, the combination with circuit interrupter having mechanical and electrical actuating mechanism with contacts engageable or disengageable thereby to close or to open the circuit, and one or more associated disconnect switches for said circuit, of means for locking the actuating mechanism to prevent actuation thereof both electrically and mechanically to prevent engagement of the contact members, a key for said locking means, said key being made available, when the actuating mechanism is locked against actuation, to permit access to or operation of the disconnect switches.

8. In an interlock system for an electrical distributing system, the combination with an electrically operable circuit breaker having a tripfree mechanism embodying a biassed latch for normally holding two members of the trip-free mechanism together in co-operating relationship, of means for preventing closure of the breaker both electrically and mechanically comprising a finger movable to engage and move the latch to non-latching position, a lock for locking the finger in such position, and a key for the lock, removable from the look only when the finger is in such latch moving position, said key being then available to provide access to an apparatus or device associated with the circuit-breaker, and being further required to unlock the finger lock before the breaker may be reclosed.

9. In a circuit breaker, the combination with contact members and actuating means therefor including a trip-free mechanism embodying two co-operative members and a latch for normally mechanically relating them, of means for controlling the breaker, when open, to prevent reclosure thereof, under certain conditions, comprising means for rendering the latch non-operative to mechanically relate the mechanical members.

10. In a circuit breaker, the combination with contact members and actuating means therefor including a trip-free mechanism embodying two co-operative members and a latch for normally mechanically relating them, of means for controlling the breaker, when open, to prevent reclosure thereof, under certain conditions, comprising a detent to hold the latch in non-operating position, a lock to lock the detent in such position, and a key removable from and insertable into the look only in such locking position.

RALPH L. KIRK. 

